The anomalous photovoltaic effect was studied in epitaxial La0.8Sr0.2MnO3 films by laser molecular beam epitaxy. It is demonstrated that the signal polarity is reversed when the films are irradiated through the substrate rather than the film. Electron microdiffration and high-resolution imaging reveal that La0.8Sr0.2MnO3 thin film is epitaxially grown on the substrate, and the oriented microdomains run through the thickness of film, forming a columnar structure. Detailed investigations of the distribution of electric potential in the film surface with respect to the location of laser spot suggest that the anomalous photovoltaic response is due to an asymmetry of oriented microdomains in thin film. Under ultraviolet laser irradiation, the electron-hole pairs are excited in the manganese oxide film. The asymmetry of microdomains generates a built-in electric field and induces an asymmetric transport of the excited carriers, and hence a a photo voltage signal is obtained.